1. Field of the Invention
The present invention relates to a compact membrane electrode assembly that can simply produce electrolyzed water containing ozone, hydrogen peroxide, hypochlorous acid, and the like at home or elsewhere and a compact or portable electrolyzed water production device using the membrane electrode assembly.
2. Description of the Related Art
The usage of electrolyzed water has been described in publications related to the establishment of the JIS standard for a household electrolyzed water production device in 2005, the hygiene management standards for school lunches and a manual related thereto that were established by the Ministry of Education, Culture, Sports, Science and Technology in 2009, and the guidelines for the Japan Food Hygiene Association published under the supervision of the Ministry of Health, Labor, and Welfare in 2009. Thus, attention has been recently focused on an electrolyzed water production device.
The term “electrolyzed water” is a generic name of an aqueous solution obtained by electrolyzing raw material water such as pure water, tap water, soft water, or a dilute saline solution by applying a direct-current voltage, the aqueous solution containing an electrolyzed product such as ozone, hydrogen peroxide, hypochlorous acid, or a mixture thereof. Electrolyzed water production devices usually have a two-chamber or three-chamber structure in which solutions or gases that are present on the anode side and the cathode side are physically separated from each other. However, in some electrolysis processes, mixing an anolyte and a catholyte together is necessary or permitted. In such a case, the electrolyzed water production device used also has a one-chamber structure accordingly.
In the case where an electrolyzed water production device has a two-chamber or three-chamber structure, “acidic electrolyzed water” is obtained on the anode side. Main components of the acidic electrolyzed water are ozone water, hydrogen peroxide water, and hypochlorous acid water. On the other hand, “alkaline electrolyzed water” is obtained on the cathode side. In the case where an electrolyzed water production device having the one-chamber structure is used, a mixture of acidic electrolyzed water and alkaline electrolyzed water is obtained as electrolyzed water.
Japanese Unexamined Patent Application Publication Nos. 2006-346203, 2008-73604, 2008-127583, 2009-125628, and 2009-138262 disclose a membrane electrode assembly and an electrolyzed water production device using the membrane electrode assembly. The membrane electrode assembly and the electrolyzed water production device are characterized in that a strip-shaped ion exchange membrane is provided around the circumference of a rod-shaped or tubular anode in the form of rings or in a spiral manner, or a tubular ion exchange membrane is provided around the circumference of a rod-shaped or tubular anode in a tubular manner, and a strip-shaped or a line-shaped cathode is wound around the surface of the ion exchange membrane in the form of rings or in a spiral manner.
The membrane electrode assembly and the electrolyzed water production device using the membrane electrode assembly have the following structure: A membrane electrode assembly is prepared by providing a strip-shaped or tubular ion exchange membrane around a rod-shaped or tubular anode, and winding a strip-shaped or a line-shaped cathode around the surface of the ion exchange membrane. The membrane electrode assembly is fixed in a tube, and a power feeding terminal is connected to the anode and/or the cathode in the tube, thus forming an electrolysis unit. This electrolysis unit, a container that stores raw material water, and a head form an electrolyzed water ejection device. Electrolyzed water produced by electrolyzing the raw material water with the electrolysis unit is ejected from the head.
According to the membrane electrode assembly and the electrolyzed water production device described in the above patent documents, the size of the device can be reduced, a raw material aqueous solution can be electrolyzed by using the compact device, and the produced electrolyzed water can be immediately ejected and used.
As described above, in the membrane electrode assembly produced by providing a strip-shaped ion exchange membrane around the circumference of a rod-shaped or tubular anode in the form of rings or in a spiral manner or providing a tubular ion exchange membrane around the circumference of a rod-shaped or tubular anode in a tubular manner, and winding a strip-shaped or a line-shaped cathode around the surface of the ion exchange membrane in the form of rings or in a spiral manner, and the electrolyzed water production device using the membrane electrode assembly, the anode, the membrane, and the cathode are integrated with each other. Accordingly, once the membrane electrode assembly is produced, the membrane electrode assembly is easily handled and can be easily installed in the device. In addition, by adjusting the diameter of the rod-shaped or tubular anode, the cross-sectional shape of the anode, the thickness and the width of the ion exchange membrane, and in the case of a line-shaped cathode, the interval of the winding, by appropriately selecting the diameter of the tube that houses this assembly to form a counter electrode chamber, and by appropriately determining the number of rod-shaped or tubular anodes used, a gas-liquid flow path suitable as an anode chamber and a cathode chamber is formed. In addition, the concentration of an electrolyte species in the electrolyzed water can be set to a desired value by changing the amount of water supplied and the current value. Furthermore, sterilization can be performed with the electrolyte species at the desired concentration by ejecting or spraying the obtained electrolyzed water onto a target object.
However, the electrolyzed water production device using the membrane electrode assembly described in the above patent documents has the following problems: Since a strip-shaped or a line-shaped cathode is wound around the surface of an ion exchange membrane in the form of rings or in a spiral manner (hereinafter, this electrode is referred to as “wound-type electrode”), it takes time to wind the line-shaped cathode around the surface of an ion exchange membrane, and it is difficult to make the strength of the winding and the interval of the winding uniform. In addition, in this wound-type electrode, the fixing performance (holding force) of the cathode wire and the ion exchange membrane may decrease. In the case where the size of the electrolyzed water production device is reduced, a skilled process is necessary for producing the device. Thus, it is difficult to mechanize the process, resulting in an increase in the production cost.
The following two methods are conceivable as a method for fixing (holding) the cathode wire and the ion exchange membrane on the wound-type diamond electrode.
(1) First Fixing Method (Non-Binding Method)
A strip-shaped ion exchange membrane is wound around an anode constituted by a rod-shaped diamond electrode, and a cathode wire is then wound around the ion exchange membrane in a spiral manner. Thus, the cathode wire is plastically deformed to fix the cathode wire and the ion exchange membrane. After the winding, the cathode wire is somewhat rewound by springback. However, due to the elasticity of the ion exchange membrane, the cathode wire and the ion exchange membrane are held on the anode constituted by a rod-shaped diamond electrode in a close contact manner.
(2) Second Fixing Method (Binding Method)
In the case where the number of windings is small or the cathode wire is thin, the force for holding the ion exchange membrane is smaller than the case described above. Therefore, rewinding is suppressed by, for example, strongly winding the cathode wire a plurality of times in a close contact manner at the beginning and at the end of winding of the cathode wire. Thus, the cathode wire and the ion exchange membrane are held on the anode constituted by a diamond electrode.
In general, from the standpoint of complication of the process and the cost, the non-binding method, which is the first fixing method, is preferably employed as the method for fixing (holding) the cathode wire and the ion exchange membrane on the anode constituted by a diamond electrode.
However, in the case where the non-binding method is employed and the size of the existing wound-type diamond electrode having a cathode wire fixed in a non-binding manner is reduced, the following problems occur: Specifically, when the number of windings of the cathode wire is reduced, the frictional force in an axial direction of the diamond electrode is decreased in accordance with the reduced number of windings. As a result, the cathode wire and the ion exchange membrane easily shift in the axial direction.
Furthermore, when the number of windings is reduced (for example, to about 1 to 3), since the beginning and the end of the winding are not bound, the holding force (pressure) of the cathode wire that presses the ion exchange membrane onto the diamond electrode decreases. Accordingly, in the case where electrolysis is performed at a certain current density using a diamond electrode having a small number of windings of the cathode wire, it is believed that the voltage of the diamond electrode becomes higher than that of the case where the number of windings of the cathode wire is larger. Thus, in the case where the existing wound-type diamond electrode is used and the number of windings of the cathode wire is reduced, it is necessary to fix both ends of the cathode wire by binding so that the cathode wire and the ion exchange membrane do not shift in the axial direction of the diamond electrode and a stable force for holding the ion exchange membrane is obtained.
On the other hand, in the case where the binding method, which is achieved by the second fixing method, is employed and the size of the diamond electrode is reduced (that is, the number of windings is reduced), the amount of material of the anode constituted by a diamond electrode and the process of the winding are reduced, thereby reducing the cost. However, the setup (the number of steps) of the process of the winding does not change. Consequently, the ratio of the cost of the process of the winding to the total cost of the diamond electrode increases. In addition, since it is necessary to fix the two ends of the cathode wire by binding, the step of binding is increased.
As described above, in the case where a compact diamond electrode is produced by reducing the number of windings in the existing wound-type diamond electrode, the production cost of the diamond electrode per the amount of O3 generated is significantly increased.
As a solution to the problems (such as destabilization in the fixing of the shape due to a decrease in the force for holding an ion exchange membrane with a cathode wire, an increase in the electrolytic cell voltage, fixing of both ends of a cathode wire for suppressing these problems, and an increase in the man-hour caused thereby) caused in the reduction in the size of the diamond electrode, the present invention provides a clip-type membrane electrode assembly in which a clip-shaped cathode is used instead of a cathode wire.